Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.
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FEATURE lated in tons per hour and those for liquid fuels in liters per hour. Some setpoints have specified limits, breaching them always leads to an increase in the proportion of the primary fuel used. If a malfunction results in the loss of one ingredient from the selected fuel mix, the missing calorific value is automatically made up from the remaining active fuel ingredients. The individual fuel feed controllers are then driven by the setpoints of the individual ingredients. There is an upstream ramp function to prevent large jumps in the setpoints for the individual controllers (scales). This means that any deviation from the existing setpoint, whether caused by the loss of a fuel, the recipe specification or by the operator, is continuously readjusted up or down back toward the input value. As previously mentioned, reliable measurement of the oxygen in the kiln is an important condition for achieving stable kiln operation. Only when this has been achieved can an appropriate process measuring technique succeed in achieving any further optimization. The process control system delivers a clear fuel mix, and a flexible assignment of the primary and secondary firing controllers. The control concept integrated in Cemat, which is based on Simatic PCS7, enabled a continuous fuel feed to be achieved. This leads to uniform kiln operation and thus highly efficient energy usage. If one fuel is lost, the heat value is automatically corrected. That is, the control system responds to malfunctions immediately to maintain uniform kiln operation, even without operator intervention. of cement, which also benefits the environment. Electricity prices make up over 50 percent of the industry's total energy costs, and they are tending to increase. For this reason, it is essential to keep these costs under control and optimize them even further. An examination of the distribution of the total electrical energy consumption across all the stages of production in a cement works reveals that the grinding mills consume almost two-thirds. The majority are raw meal and cement mills, designed as either vertical or ball mills. Cement production runs continuously with very limited reserve capacities and little redundant plant or equipment. The greater part of the equipment therefore has to run around-the-clock or – if there are specific restrictions – throughout the day. Electricity costs can be reduced by shifting production – especially in the cement mill section – to cheaper offpeak periods and by ensuring that the contractually agreed energy consumption limits are not exceeded. The load-management function integrated into the control system enables increased consumption by hidden electricity guzzlers to be counteracted by, for example, automatically shutting down auxiliary processes if there is a danger of exceeding the limit. This not only reduces energy costs but also stabilizes the power distribution system by avoiding the need for peak load power from the public grid or the company's own power generating plants. The best tools for finding optimization strategies are the "PowerControl" and "power rate" add-ons for the This method of kiln operation not only saves energy but also minimizes emissions and keeps within limit values. Uniform kiln operation also guarantees better clinker quality. The use of an average 75 percent proportion of secondary fuels has enabled the consumption of fossil fuels to be substantially reduced. This high proportion puts Rohrdorf cement plant in a leading position. INTEGRATED ENERGY MANAGEMENT Alongside fossil energy, electrical energy also plays a major role in the cement industry, especially in raw material preparation and cement milling. The German cement industry consumes approximately 3.3 million megawatt hours of electrical energy per annum. About 100 kWh of electrical energy are used per ton 10 CEMENT AMERICAS • Fall 2013 • www.cementamericas.com